Explosion rivet



Oct. so, 1945. L, A, BURRQWS 2,387,742

EXPLOS ION RIVET Filed Aug. l12, 1942 WZMM@ aww..

.Patented Oct. 30, i945 aime EXPLOSION RIVET Lawton A. Burrows, Woodbury, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application August 12, 1942, Serial No. 454,561'

v(Cl. 85-37) 3 Claims.

This invention relates to the art of explosively blasting a contact between objects.

The present application is a continuation. in part of my copending application Serial No 274,771, filed May 20, 1939.

The original application discloses an explosive rivet charged with a detonating explosive capable oi initiation by means of an electrostatic discharge of 100,000 ergs.

The object of the present invention is to apply this principle not only to explosive rivets but t any explosive metal connecting element. A further object is to apply the principle to ^haste-ning one or more articles. Additional objects will be disclosed in the following detailed description of the invention.

According to my invention a recess or perforation 1s formed in the article or articles to be joined or fastened and the metal fastening element is inserted in said recess. The metal fastening element contains a charge of'a detonating explosive composition capable of initiation by means of a spark discharge including a high voltage spark, electrostatic discharge and the like.

When the joining, riveting, or fastening is to be performed, the explosive is ignited, preferably by means of an electrical conductor introduced into the cavity in the connector element such as a rivet, bolt or fastener and connected to a source of relatively high voltage electricity. This inserted electric conductor will desirably be insulated except at its terminal point. With this conductor suiiiciently close to the bottom of the rivet, bolt, or connector cavity in the vicinity of the explosive charge, the circuit may be closed by the throwing of a switch, and a spark jumps across the' gap between the conductor and the metal of the connector element or rivet, thereby bringing about the explosion.

In order to describe my invention more clearly, reference is made to the accompanying drawing. Figure 1 illustrates an explosion rivet in position for riveting together two metal sheets. Figure 2 shows the same rivet after the explosion. Figure-3 shows another design `of explosion rivet before spreading, while Figure 4 illustrates the same rivet after expansion. Figure 5 represents a rivet of the countersunk type, after expansion, but otherwise similar to the one in Figure 4. Figure 6 shows an explosive bolt loaded with explosive accordingl to my invention. Figure 7 shows a threaded explosive bolt already led by means of a spark and expanded within a cavity in a metal plate according to my invention. Figure 8 shows an explosive electric cable connector loaded with spark sensitive detonating explosive. Figure 9 shows an explosive electric connector element already fired by static means and thus expanded within a metalplate.

According to my invention, the connecting operation such as a riveting operation is carried out in the following manner. As shown in Figure 1, the shank 2 of the rivet is inserted through the drill hole in the two metal sheets 5 and which are to be joined together. When in place, the head l of the rivet rests firmly against the nearest metal sheet. Within the cavity 3, in the shank of the rivet, a small charge is loaded of a detonating explosive capable of explosion by a. spark discharge and very sensitive to such electric discharge. The explosion is'brought about by introducing into the cavity. a metal conductor connected to a source of high voltage electricity. The riveting effect will be apparent from Figure 2, where the bulging of the walls of the rivet shank is seen to have caused compression together of the metal sheets.

The rivet shown in Figure 1 was adapted to receive the explosive charge in a. recess in the shank, opening at the base of the rivet.l A different type of rivet is shown in Figure 3, which has a number of advantages over that previously described, and which is described in the cependine case of Burrows and Lawson (Serial No. 274,772, filed May 20, 1939). In this type, the cavity within the rivet 'is made by boring or entering through the head l. A relatively long and narrow cavity results. The explosive charge ls shown at 2, and ignition is brought about by means of the insulatedwire l which is connected with a source of high voltage electricity and which is introduced into the recess in the rivet and is caused to discharge a spark yto the walls of said recess in the vicinity of the spark-sensitive explosive charge, when the circuit is closed. The bulging effect on the rivet walls is shown in Figure 4, and this is very effective in holding the two metal sheets tightly together. With either type of rivet it will be desirable that at least part of the explosive charge in the rivet cavity be' slightly beyond the surface of the metal sheet on the side opposite to the head of the rivet,

The same principle is shown in the remaining iigures as applied to explosive bolts and electrical connectors. The electric discharge is applied to the explosive within the bolt or element which being susceptible to static is red expanding the metal surrounding it to effect a tight junction. vWhile my invention will be described particularly with reference to riveting, it will be understood that'the principles apply as well to boltins. loining and fastening and connecting', as shown in these gures.

In the foregoing it is stated that `a high voltage spark is utilized to bring about explosion. The explosive used according to my method is l one which is capable of ignition by such a spark.

v a metal cavity, it is evident that there is no danger of static accumulation in the vicinity f the charge. The source of electricity for the tiring spark will ordinarily be, a condenser of suitable capacity, an induction coil, or regular power or lighting circuits where suitable transformers or other device have been introduced to give the desired control over the firing source. A diier ence of potential of around 2.000 volts and an energy output of a low order of magnitude are satisfactory conditions.

It is known that explosion" rivets have been employed in the prior art. A preferred method of bringing about explosion has been by the application of heat to the rivet head. While such a method is eiective, I find my method of spark ignitionlto have many vadvantages in the way of time-saving, convenience in operation, simplicity of equipment, and the like. When indirect heating is employed, a time lag of several seconds occurs between application of the heat and the moment of explosion; likewise, there isa 'loss of energy. In addition, the heating up of the metal sheets may be undesirable. With the spark'ignition method of my invention, ignition-is instantaneous, the energy is applied intensively,

and only a very small amount of energy is quired. J

As shown in Figures 3. and '4 of the drawing,l

my preferred form of rivet has the entrance to the recessed cavity by meansofA a drillhole through the head of the rivet. With this*A type ofl rivet, my methods of vloading and ring give an evengreater advantage with regard to accessibility, since many rivets are usedln positions where approach to the iar side is dlicult, if not .impossible.

It has been stated in the foregoing thatfexplm' sives of the type of lead styphnate are well suited for employment according to my invention, 'and' compositions' containing this compound las an ingredient are equally suitable. I'nnd, 'forexample, that a composition comprising '10.parts'of leadazide, 20 parts of lead styphnate, and 10 parts of tetryl functions verysatisfactorily. Other compositions are likewise adopted for use which are themselves readily sparksensitive or contain an ingredient which is spark-sensitive and whch,.therefore, imparts thischaracterlstlc to the entire composition. Ereferably, I employ an explosive charge which is capable of ignition'- by an electrostatic. discharge .of an energy amounting to 100,000 ergs, or less. This energy requirement is detengined by a test in which a' layer of the explosi eof 0.010" thickness is spread .on a steel plate and separated by aY short gap from a steel needle. This needlel is so arranged that it can be thrown into a closed circuit with a condenser of known capacity, on which a controlled voltage can be imposed. In this way a spark of the desired energy content can be caused to jump the gap from needle to plate at the locus of the explosive layer. Operating according to this arrangement, approximate electrostatic energy requirements inergs for ignition of various explosives were determined as follows:

Lead styphnate 500 Copper acetylide 50!) Lead nitrato-hypophosphite 500 Lead azide (commercial) 200,000

While the preferred compositionsfor use in rivets according to my 'invention have relatively low energy requirements for ignition, many other materials will be satisfactory for use having much higher requirements, thoughin all cases below 100,000 ergs.

The amount of explosive charge for satisfactory results will depend upon the nature-of the` explosive, the size of the rivet, and the material of which the rivet is constructed. With an aluminum rivet having a recess of 11s" diameter, av 0.4 grain charge of a lead azide-lead styphnate composition may be satisfactory, whereas, with larger rivets and increased size. of preformed cavity, a charge ten times as great may possibly be employed. Composite charges may likewise be used also, if desired, especially in the larger size rivets, for example, using in addition to the primary charge, a base charge of tetryl or other suitable material.

It will be understood that many different sizes of rivets may be employed according to my lnvention, depending on the type'of work to be per'- 'formed, andthat such rivets may be of any of the commonv metals which have the properties of strength and malleability adapted to make them serviceable in such use. Copper, aluminum, and iron, and their alloys, may be cited as examples of sutable metals, though the use of copper and azides together is generally undesirable. Whlle my invention has been directed to the joining of two metal sheets by means of rivets, it isapparent that more than two sheets may be Joined in such manner, if desired.

In describing my process of riveting with use of explosive charges, it has beenstated that the explosive is introduced into the bottom of the recessed cavity in the rivet. vWhile we donot wish to be limited as to the method of introducing the explosive charge, my preferred method comprises 'extruding the charge' into place in plastic form from a closed container. for example from a thin-walled collapsible tube. 'I'his method has l the advantage of convenience and safety in hanf dling the' explosive composition. The extruded charge remains in place where vdeposited and hardens on subsequent evaporation of solvent.

This hardening or setting requires a certain interval of time, hence the loading of the rivets will desirably take place previous to their in.ser

Ation into the sheets to be riveted. Any ot the explosive compounds mentioned as applicable can be handled and extruded in the manner described by. treatment with the desired plasticity. Y i In the case of large. rivets, or fasteners, it is desirable first -to charge the explosive into a cylindrical metal shell and introduce this shell into a cavity in the connector prior torexplosion.

A satisfactory method/.of preparing the explosive charge for extrusion and for obtaining the he proper solvent to give Y aseavca desired viscosity is by blending with nitrccotton gelatinized by a suitable solvent.

My invention and method of riveting have been described at some length in the foregoing. It will be understood, however, that many variations may be made in details of procedure and design without departure from the scope of the invening open from the end of the element to the explosive charge. v

2.4m explosion rivet adapted to join at least two objects with surfaces in contact bybeing 4min a hole extending through said objects, said explosion rivet comprising a metal rivet. a cavity extending longitudinalLv through the head and into the shank of said rivet, and a detonating explosive charge 7 capable of being ig' nited by an electrostatic discharge of 100,000 ergs disposed in said cavity, partly in that portion oi' the cavity in the shank of the rivet adapted to extend through and beyond said metal objects,

and partly within that portion of said cavity in l the shank positioned within vthe hole in said objects, said rivet being open from the head end to the explosive charge.

3. An explosion rivet adapted to join at least -two metal objects with surfaces in contact by being disposed in a hole extending through said objects, said explosion rivet comprising a metal rivet, a cavity extending longitudinally through the head and into the shank of said rivet, and a detonating'explosive charge comprising a. staticsensitive explosive compound selected from the group consisting of lead styphnate, basic lead` picrate, silver azide, copper acetylide, and lead nitrato-hypophosphite disposed in said cavity, partly in that portion of the cavity in the shank of the rivet adapted to extend .through and beyond said metal objects, and partly within that portion of said cavity in the shank lpositioned within the hole in said objects, said rivet being open from the head end to the explosive charge.

LAWTON A. BWS. 

